While the pair were going at it, the camera lingered on a sad-looking Tyrion as he loitered suspiciously in the hallway outside, The Sun reports.

As Dany and Jon romped, Tyrion loitered in the hallway. Foxtel

He can be seen pulling an odd and ominous face as Dany and Jon romp in the next room, and fans think there may be significant reason why.

Earlier in the feature-length episode, Tyrion spends some alone time with his murderous sister Cersei, where he ends up making a deal to secure a truce between Dany and The Crown.

He also reveals that he doesn't want to destroy his family, and told Cersei how much he loved her children, Tommen and Myrcella.

And some viewers think that this conversation may explain why he looked so dodgy when he was loitering outside Dany's room.

Dany and Jon finally got it on.Foxtel

In the books, Daenerys's ultimate fate is foreshadowed by a prophecy, which claims she will face three devastating betrayals. One betrayal will be for blood, the second will be for gold and the third will be for love.

Now fans believe Tyrion's chat with Cersei in the season seven finale could lead to one of those betrayals. They think he might have cut a deal with his sister off screen, after the scene ended.

Lena Headey as Cersei Lannister in a scene from season 7 episode 7 of Game of Thrones. HELEN SLOAN / HBO

Since Tyrion knew Cersei was never really going to head north to fight the White Walkers, he told her to lie about it, the theory goes.

Notably, just moments earlier, he had lectured Jon on the importance of knowing how to lie: "Have you ever considered learning how to lie every now and then?" By convincing Cersei to lie, Tyrion would give the Lannisters a chance to take back control of Westeros while Dany's armies were in the north.

Granted, Tyrion and Cersei hate each other, so it would be a stunning twist. But it would also explain why Tyrion looked so sad at the end of the episode, as the reality of his treason started to dawn on him.

Peter Dinklage in a scene from the season 7 finale of Game of Thrones. Foxtel

Another, less sensational theory suggests Tyrion is worried about Dany getting pregnant, since he is so worried about what happens to Westeros after she dies.

Could it be that he's eyeing the throne for himself? Is he plotting to tear down the monarchy once she's gone? Or is it just genuine concern from her right-hand man?

We'll have to wait a long time to find out.

This story originally appeared in The Sun and has been republished here with permission.